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Source and destination data buffers are allocated with GPF_KERNEL flag. It means that, if the DDR is more than 2GB, buffers can be allocated above the 32-bit addressable space. In this case, and if the dma controller is only 32-bit compatible, swiotlb bounce buffer, located in the 32-bit addressable space, is used and introduces a memcpy. To prevent this extra memcpy, due to swiotlb bounce buffer use because source or destination data buffer is allocated above the 32-bit addressable space, force source and destination data buffers allocation with GPF_DMA instead, when nobounce parameter is true. Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com> Link: https://lore.kernel.org/r/20231124160235.2459326-1-amelie.delaunay@foss.st.com Signed-off-by: Vinod Koul <vkoul@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.